1. Field of the Invention
The present invention relates to a semiconductor device utilizing a plasmon phenomenon and an electronic apparatus such as a camera having a solid-state imaging device constituted by such a semiconductor device.
2. Description of the Related Art
Recently, keen attention is paid to special light referred to as surface plasmons attributable to intense electric fields generated in microscopic regions as a result of coupling between light and a metal-type material such as gold, silver, copper, or aluminum occurring under special conditions. In practice, applications of such a phenomenon are actively pursued in biological fields, the applications including SPR microscopes in which a combination of a Kretschmann configuration and attenuated total reflection is used to observe absorption of monomolecules such as protein monomolecules. Attenuated total reflection may be abbreviated as “ATR”, and “SPR” is the abbreviation of surface plasmon resonance.
Techniques for reducing the thickness of photodiodes of image sensors (so-called solid-state imaging devices) and improving the sensitivity of the photodiodes taking advantage of plasmons have been proposed (see JP-A-2009-38352 and JP-A-2009-147326 (Patent Documents 1 and 2)).
FIGS. 14A and 14B show image sensors described in Patent Document 1. Basically, the image sensors have plasmon resonators (metal particles) embedded therein, which allows the sensors to be provided with a small thickness and a spectroscopic function acting in the depth direction thereof. An image sensor 101 shown in FIG. 14A has an n-type semiconductor region 103, a p-type semiconductor region 104, and another n-type semiconductor region 105 formed in the order listed on a p-type semiconductor substrate 102 to provide a photoelectric conversion layer having p-n junctions on. Plasmon resonators 106 which undergo plasmon resonance with red light R are embedded in the p-type semiconductor substrate 102. Plasmon resonators 107 which undergo plasmon resonance with green light G are embedded in the n-type semiconductor region 103. Plasmon resonators 108 which undergo plasmon resonance with blue light B are embedded in the p-type semiconductor region 104. Each of the plasmon resonators 106, 107, and 108 is coated with a transparent insulation film 109. Light L enters the photoelectric conversion layer having p-n junctions, and red, green, and blue beams of light enter the plasmon resonators 106, 107, and 108. When the plasmon resonators undergo plasmon resonance with the light beams incident thereon, the red, green, and blue light beams are localized in small areas in the vicinity of the plasmon resonators 106, 107, and 108. Electrical charges generated by light beams reemitted from those areas are accumulated, and resultant signals are read out by a readout section 111.
An image sensor 113 shown in FIG. 14B has photoelectric conversion layers 115, 116, and 117 which are insulated from each other by transparent insulation films 114. Plasmon resonators 106, 107, and 108 which undergo plasmon resonance with red light R, green light G, and blue light B are embedded in the photoelectric conversion layers 115, 116, and 117, respectively. Each of the plasmon resonators 106, 107, and 108 is coated with a transparent insulation film 109. Electrodes 118A and 118B to serve as readout sections are formed on both ends of each of the photoelectric conversion layers 115, 116, and 117. Light L enters the photoelectric conversion layers 115, 116, and 117, and red, green, and blue beams of light are enhanced by the plasmon resonators 106, 107, and 108. Electrons which have been excited from the valence band into the conduction electron band as thus described are read out as signals through the electrodes 118A and 118B.
A sensor can be provided with a smaller thickness without any reduction in sensitivity by using a configuration as thus described in which a plurality of photoelectric conversion layers having plasmon resonators disposed therein are formed one over another. The sensor can be provided with a color separating function acting in the depth direction thereof because the resonance peaks of the plasmon resonators disposed in the respective photoelectric conversion layers reside in different wavebands and the resonators therefore serve as spectroscopic elements.
The intensities of light beams cannot be detected when the light beams are simply absorbed in the plasmon resonators disposed at different depths of the resonator. The intensities of light beams in the respective wavebands associated with the resonance peaks of the plasmon resonators can be detected because light beams reemitted from the plasmon resonators are photo-electrically converted by materials surrounding the resonators to convert the intensities of the incident light beams into mounts of electrical charges. The amounts of electrical charges may be acquired in the form of voltages or currents using p-n junctions and electrodes, whereby the intensities of light beams in the respective wavebands can be obtained as electrical signals.
FIGS. 15A and 15B show an image sensor described in Patent Document 2. Basically, the sensor includes metal nanoparticles disposed on a silicon surface to utilize the plasmon phenomenon, and the shapes and positions of the nanoparticles are designed to provide the sensor with a small thickness and a spectroscopic function. Specifically, an image sensor 121 shown in FIGS. 15A and 15B is formed by disposing a patterned layer 125 of metal microparticles 124 through a dielectric film 123 on a top surface of a p-n junction photodiode 122 made of silicon. The dielectric film 123 is made of SiO2, SiON, HfO2, Si3N4 or the like, and the dielectric film 123 has a thickness of 3 nm to 100 nm.
Metal microparticles 124 are particles of at least one type of metal selected from among a group including gold, silver, copper, aluminum, and tungsten. The patterned layer 125 of the metal microparticles 124 has a plurality of regions, and each region of the patterned layer 125 of the metal microparticles 124 is formed by a plurality of sub pixel regions, i.e., a red sub pixel region 126R, a green sub pixel region 126G, and blue sub pixel regions 126B. The metal microparticles 124 in the sub pixel regions 126R, 126G, and 126B have respective sizes descending in the order in which the regions are listed. The metal microparticles 124 may have triangular, square, pentagonal, circular, and star-like shapes, and the patterned layer 125 is formed such that optimum plasmon resonance will occur between the microparticles and light beams having particular wavelengths.
Plasmons are formed as a result of resonance between electro magnetic waves of light beams and electrons on the surface of the metal microparticles 124 of the patterned layer 125, whereby the light beams stay in the vicinity of the metal microparticles 124 for a long time. Thus, such a phenomenon or effect of the pattern layer 125 allows the time available for the photodiode diode to detect light incident on the same to be increased, whereby improved sensitivity can be achieved.